Compact high-voltage power supply and radiation apparatus systems and methods

ABSTRACT

A apparatus may include a power supply to receive a first voltage potential and output a second voltage potential that is greater than the first voltage potential and a cathode emitter to emit ions in response to application of the second voltage potential. The apparatus may also include a step down transformer to receive the second voltage potential and output a third voltage potential that is less than the second voltage potential. The apparatus may also include a heating element to, in response to application of the third voltage potential, heat the cathode emitter and lower a work function of the cathode emitter.

BACKGROUND

This disclosure relates generally to systems and methods for a compacthigh-voltage power supply and radiation apparatus, for example, as usedin downhole tools. Furthermore, although discussed herein in the contextof downhole tools, the discussed techniques may be applicable in anysuitable radiation apparatus.

This section is intended to introduce the reader to various aspects ofart that may be related to various aspects of the present techniques,which are described and/or claimed below. This discussion is believed tobe helpful in providing the reader with background information tofacilitate a better understanding of the various aspects of the presentdisclosure. Accordingly, it should be understood that these statementsare to be read in this light, and not as an admission of any kind.

Generally, an electrically operated radiation apparatus, such as anx-ray apparatus, a gamma ray apparatus, or a neutron apparatus, maygenerate radiation using electrical power to facilitate determiningcharacteristics of the surrounding environment, such as a geologicalformation. Thus, radiation apparatus may be used in various contexts,such as a downhole tool or for material analysis. In some scenarios, ahigh-voltage power supply and/or a cathode heater power supply may beimplemented to achieve the high energy radiation. For example, a chargedparticle beam of electrons or other ions may be emitted from a cathodeand accelerated by electric fields, such as in a particle accelerator,into a target to generate radiation such as neutrons or x-rays. In someinstances, such electronic radiation apparatus are used in downholewell-logging tools to take measurements of a geological formation. Theradiation may exit the downhole tool and proceed into the geologicalformation, and measurements of the radiation that return to the downholetool may provide an indication of where hydrocarbon resources may belocated, as well as other characteristics of the geology of theformation. In some scenarios, the measurements of the radiation thatreturns to the downhole tool may depend on the amount of radiation thatwas initially emitted by the radiation apparatus. As such, providing amore consistent or predictable supply of radiation may allow for a moreaccurate and/or precise measurement.

Given the size limitations on downhole tools, the power supplies andradiation apparatus may be packaged in a relatively small housing.Further, as stated above, a radiation apparatus may use a cathodeemitter to produce electrons in the form of an electron beam. However,in some scenarios, such as for a hot cathode, the cathode emitter mayuse a separate power supply (e.g., separate from the high-voltage powersupply) along with a transformer to power the cathode heater, which mayincrease the diameter of the tool.

SUMMARY

A summary of certain embodiments disclosed herein is set forth below. Itshould be understood that these aspects are presented merely to providethe reader with a brief summary of these certain embodiments and thatthese aspects are not intended to limit the scope of this disclosure.Indeed, this disclosure may encompass a variety of aspects that may notbe set forth below.

An electrically operated downhole tool, such as a nuclear radiationapparatus, may generate radiation (e.g., x-rays, gamma rays, neutrons,etc.) using electrical power to facilitate determining characteristicsof its surrounding environment. To achieve the high energy radiation, ahigh-voltage power supply such as a voltage multiplier (e.g., aCockcroft-Walton high-voltage ladder or other suitable voltagemultiplier) may be implemented to bias a cathode emitter of a beaminjector to create an ion beam. Additionally, in some embodiments, thehigh-voltage generated by the high-voltage power supply may be steppeddown to also power a hot cathode heater.

Additionally or alternatively, the beam injector may also include anelectrode to bias at least a portion of the electrons to remain on thecathode emitter and focus the emitted electrons into an electron beam.The beam injector may also include a resistor coupled between thecathode emitter and the electrode and configured to allowself-regulation of a voltage potential on the electrode based at leastin part on a current of the electron beam. The self-regulation of thevoltage potential may allow for more accurate and precise ion beam foreither a hot cathode or a cold cathode.

In one embodiment, an apparatus may include a power supply to receive afirst voltage potential and output a second voltage potential that isgreater than the first voltage potential and a cathode emitter to emitions in response to application of the second voltage potential. Theapparatus may also include a step down transformer to receive the secondvoltage potential and output a third voltage potential that is less thanthe second voltage potential. The apparatus may also include a heatingelement to, in response to application of the third voltage potential,heat the cathode emitter and lower a work function of the cathodeemitter.

In another embodiment, a method comprising may include receiving a powerinput at a first voltage potential and increasing, via a voltagemultiplier, the first voltage potential to a second voltage potential.The method may also include decreasing, via a transformer, the secondvoltage potential to a third voltage potential. The method may alsoinclude providing the second voltage potential to a cathode emitter andproviding the third voltage potential to a heating element of thecathode emitter.

The another embodiment, a downhole tool may include a radiationapparatus that has a cathode emitter to emit electrons and an electrodeto bias at least a portion of the electrons to remain on the cathodeemitter and focus the electron into an electron beam. The downhole toolmay also include a resistor coupled between the cathode emitter and theelectrode to allow self-regulation of a voltage potential on theelectrode based at least in part on a current of the electron beam. Thedownhole tool may also include a high-voltage power supply comprising avoltage multiplier to supply power to the cathode emitter at a voltagepotential.

Various refinements of the features noted above may be undertaken inrelation to various aspects of the present disclosure. Further featuresmay also be incorporated in these various aspects as well. Theserefinements and additional features may exist individually or in anycombination. For instance, various features discussed below in relationto one or more of the illustrated embodiments may be incorporated intoany of the above-described aspects of the present disclosure alone or inany combination. The brief summary presented above is intended tofamiliarize the reader with certain aspects and contexts of embodimentsof the present disclosure without limitation to the claimed subjectmatter.

BRIEF DESCRIPTION OF THE DRAWINGS

Various aspects of this disclosure may be better understood upon readingthe following detailed description and upon reference to the drawings inwhich:

FIG. 1 is a schematic diagram of a well site system that may employ abeam injector in a downhole tool, in accordance with an embodiment;

FIG. 2 is a block diagram of the downhole tool that may employ the beaminjector in a radiation apparatus, in accordance with an embodiment;

FIG. 3 is a schematic cross-section of the radiation apparatus includingthe beam injector and a particle accelerator, in accordance with anembodiment;

FIG. 4 is a schematic diagram of three operational regimes of the beaminjector with associated potential lines as well as a cathode heatercurrent, beam focus, and beam current at each of the operationalregimes, in accordance with an embodiment;

FIG. 5 is a schematic circuit diagram of the beam injector thatself-regulates a potential on an electrode, in accordance with anembodiment;

FIG. 6 is a graph of the beam current and beam focus in relation to thecathode heater current and the accelerator potential, in accordance withan embodiment;

FIG. 7 is a flowchart of an example process for calibrating andoperating the beam injector, in accordance with an embodiment;

FIG. 8 is a schematic diagram of a downhole tool, in accordance with anembodiment;

FIG. 9 is a schematic diagram of a downhole tool, in accordance with anembodiment; and

FIG. 10 is a flowchart of an example process for powering a radiationapparatus, in accordance with an embodiment.

DETAILED DESCRIPTION

One or more specific embodiments of the present disclosure will bedescribed below. These described embodiments are examples of thepresently disclosed techniques. Additionally, in an effort to provide aconcise description of these embodiments, features of an actualimplementation may not be described in the specification. It should beappreciated that in the development of any such actual implementation,as in any engineering or design project, numerousimplementation-specific decisions may be made to achieve the developers'specific goals, such as compliance with system-related andbusiness-related constraints, which may vary from one implementation toanother. Moreover, it should be appreciated that such a developmenteffort might be complex and time consuming, but would still be a routineundertaking of design, fabrication, and manufacture for those ofordinary skill having the benefit of this disclosure.

When introducing elements of various embodiments of the presentdisclosure, the articles “a,” “an,” and “the” are intended to mean thatthere are one or more of the elements. The terms “comprising,”“including,” and “having” are intended to be inclusive and mean thatthere may be additional elements other than the listed elements.Additionally, it should be understood that references to “oneembodiment” or “an embodiment” of the present disclosure are notintended to be interpreted as excluding the existence of additionalembodiments that also incorporate the recited features.

The exploration of what lies beneath the ground may be accomplished by anumber of methods including surface and downhole techniques. Thediscovery and observation of resources using downhole techniquesgenerally takes place down in the wellbore with downhole tools. Thesedownhole tools may be a part of a tool-string that may be attached to adrill or other downhole device.

One particular type of downhole tool may include an electricallyoperated radiation apparatus for generating nuclear radiation (e.g.,neutrons, gamma rays, x-rays, etc.) to facilitate determiningcharacteristics (e.g., porosity, density and/or mineralogy) of theformation. As used herein, nuclear radiation shall include radiation ofnuclear particles and/or photonic particles. Depending on the desiredcharacteristics to be determined, various types of electrically operatedradiation apparatus s may be used, such as x-ray apparatus s, gamma rayapparatus s, or neutron apparatus s. For example, in a downhole tool, aradiation apparatus may facilitate determining the porosity ofsurrounding formations, based at least in part on counts (e.g., numberof neutrons or gamma-rays) of radiation, density of surroundingformation, based on photon counts and/or determining the mineralogy ofsurrounding formations, based at least in part on a spectrum ofradiation measured by a detector (e.g., scintillator).

Nevertheless, the different types of electrically operated radiationapparatus s may use high-voltage power supplies to facilitate thegeneration of the nuclear radiation. For example, high-voltages may beused to produce electric fields to accelerate a particle (e.g.,electron, ion, or other charged particle) toward a target. When theparticle strikes atoms of the target, nuclear radiation may be generatedand output from the downhole tool. The radiation may then interact withatoms in the surrounding environment (e.g., the formation) and aresponse detected.

Charged particles (e.g., electrons or other ions) may be generated froma variety of sources for a variety of uses. In particular, it may bedesired to generate a focused beam of charged particles such that thecharged particles are emitted in generally the same direction. Forexample, a beam injector may emit the charged particle beam foracceleration via a particle accelerator for use in a radiationgeneration. In the radiation apparatus, a charged particle beam ofelectrons or other ions may be accelerated (e.g., via electric fields)into a target to generate radiation such as neutrons or x-rays. In someinstances, such electronic radiation apparatus s are used in downholewell-logging tools to take measurements within a wellbore of ageological formation. The radiation may exit the downhole tool andproceed into the geological formation. The response of the geologicalformation to the emitted radiation may be used by the downhole tool toassess properties of the geological formation, and may indicate thepresence or absence of hydrocarbons or other elements at particularlocations in the geological formation that surrounds the wellbore. Thedownhole tool may also use the radiation to identify other properties ofthe geological formation, such as porosity, lithology, density, and soforth. As should be appreciated, although described herein as applyingto radiation apparatus s for downhole tools, embodiments of the presentdisclosure may also apply to any suitable beam injector, high-voltagepower supply, and/or radiation apparatus.

In one embodiment, the beam injector may generate a charged particlebeam and utilize a Wehnelt electrode to stabilize and/or focus thecharged particle beam. Further, in some embodiments, the beam current(e.g., the amount of charged particles being emitted) and beam optics(e.g., the direction, focusing, and/or collimation of the chargedparticle beam) may be controlled such that current surges may beminimized and/or the charged particle beam maintains focus with minimalcharged particles straying from the desired beam path. Moreover, theWehnelt potential may be self-regulated based on the beam current tomaintain the desired beam current and the desired beam optics. Theself-regulated beam injector may utilize a cold cathode or a hotcathode.

In the case of the hot cathode, a power source may provide electriccurrent to heat the cathode such that energy may be imparted toelectrons on the surface of the cathode emitter to overcome the electronwork function of the cathode material and assist in the generation ofelectrons. In some embodiments, the high-voltage power supply mayinclude a step down transformer to power the cathode heater instead ofhaving a dedicated power supply and isolation transformer, which maytake up additional space within the downhole tool.

With the foregoing in mind, FIG. 1 illustrates a well-logging system 10that may employ the systems and methods of this disclosure. Thewell-logging system 10 may be used to convey a downhole tool 12 througha geological formation 14 via a wellbore 16. In the example of FIG. 1,the downhole tool 12 is conveyed on a cable 18 via a logging winchsystem (e.g., vehicle) 20. Although the logging winch system 20 isschematically shown in FIG. 1 as a mobile logging winch system carriedby a truck, the logging winch system 20 may be substantially fixed(e.g., a long-term installation that is substantially permanent ormodular). Any suitable cable 18 for well logging may be used. The cable18 may be spooled and unspooled on a drum 22 and an auxiliary powersource 24 may provide energy to the logging winch system 20 and/or thedownhole tool 12. Furthermore, the downhole tool 12 may be used in anysuitable wellbore 16, such as a wellbore 16 with or without a casing 25.

Moreover, while the downhole tool 12 is described as a wireline downholetool, it should be appreciated that any suitable conveyance may be used.For example, the downhole tool 12 may instead be conveyed as alogging-while-drilling (LWD) tool as part of a bottom-hole assembly(BHA) of a drill string, conveyed on a slickline or via coiled tubing,and so forth. For the purposes of this disclosure, the downhole tool 12may be any suitable downhole tool that uses a beam injector and/orparticle accelerator, such as a radiation apparatus (e.g., a neutronapparatus, x-ray apparatus, etc.).

The downhole tool 12 may receive energy from an electrical energy deviceor an electrical energy storage device, such as the auxiliary powersource 24 or another electrical energy source to power the tool.Additionally, in some embodiments the downhole tool 12 may include apower source within the downhole tool 12, such as a battery system orhigh voltage power supply to provide sufficient electrical energy toactivate the radiation apparatus and/or record the response of thegeological formation to the emitted radiation.

Control signals 26 may be transmitted from a data processing system 28to the downhole tool 12, and data signals 26 related to radiationmeasurements may be returned to the data processing system 28 from thedownhole tool 12. The data processing system 28 may process theradiation measurements to identify certain properties of the wellbore 16(e.g., porosity, permeability, relative proportions of water andhydrocarbons, and so forth) that may be otherwise indiscernible by ahuman operator. The data processing system 28 may be any suitableelectronic data processing system. For example, the data processingsystem 28 may include a processor 30, which may execute instructionsstored in memory 32 and/or storage 34. As such, the memory 32 and/or thestorage 34 of the data processing system 28 may be any suitable articleof manufacture that can store the instructions. The memory 32 and/or thestorage 34 may be read-only memory (ROM), random-access memory (RAM),flash memory, an optical storage medium, or a hard disk drive, to name afew examples. A display 36, which may be any suitable electronicdisplay, may display images generated by the processor 30. The dataprocessing system 28 may be a local component of the logging winchsystem 20 (e.g., within the downhole tool 12), a remote device thatanalyzes data from other logging winch systems 20, a device locatedproximate to the drilling operation, or any combination thereof. In someembodiments, the data processing system 28 may be a mobile computingdevice (e.g., tablet, smart phone, or laptop) or a server remote fromthe logging winch system 20.

One example of the downhole tool 12 is shown in FIG. 2. The downholetool 12 may include a radiation apparatus 38 to emit radiation 40 (e.g.,neutrons, x-rays, etc.) into the geological formation 14. As should beappreciated, the radiation apparatus 38 may be any suitable apparatus ofnuclear radiation. For example, the radiation apparatus 38 may be anx-ray apparatus, a neutron apparatus, a pulsed neutron apparatus, orapparatus of other desired nuclear radiation. The radiation apparatus 38emits radiation 40 out of the downhole tool 12 and into the geologicalformation 14, where it may scatter or collide with atoms of thegeological formation 14 to generate secondary radiation (e.g., gammarays) that also may scatter. Some of the radiation 40 or secondaryradiation that results from interactions with the radiation 40 mayreturn to the downhole tool 12, and be detected by a radiation detector42. In general, the radiation detector 42 may detect counts and/orenergy levels of the radiation 40 and/or secondary radiation andgenerate an electrical signal indicative of a count rate of the detectedradiation or a spectrum of detected radiation that may provide anindication of characteristics of the wellbore 16 or the geologicalformation 14.

FIG. 3 is a schematic cross-section of an example radiation apparatus 38including a beam injector 44 and a particle accelerator 46 disposed witha generally cylindrical housing 48. The housing 48 may contain a cathodeemitter 50, a target 52, an acceleration chamber 54 and/or a focusingchamber 56. In some embodiments, the interior of the housing 48 may becoated with an insulating material, such as Al₂O₃, which has a highsecondary electron emission coefficient. The insulating material mayassist in electrically separating electrodes 58 of the accelerationchamber 54 and/or the focusing chamber 56. As discussed herein, it maybe desired to maintain focused beam optics to limit the likelihood ofthe charged particles hitting the electrodes 58 or the insulatingmaterial, which may create short-circuit paths between the electrodes 58if the charged particles (e.g., electrons) sputter against the walls ofthe housing 48.

In some embodiments, a heating element 60 may be disposed proximate thecathode emitter 50 to heat the cathode emitter 50 and provide thecharged particles enough thermal energy to overcome the work functionassociated with emitting a charged particle. In one embodiment, thecathode emitter 50 may be formed of or include an emissive layer of athermionic emission material such as yttrium oxide, lanthanumhexaboride, or any suitable material that readily emits chargedparticles, such as electrons 62, when heated. Furthermore, the cathodeemitter 50 may also include a protective layer with a relatively highwork function compared to that of the thermionic emission material. Insome embodiments, the protective layer may coat the cathode emitter inareas where emission is not desired. Furthermore, the cathode emitter50, including the thermionic emission material and/or the protectivelayer, may be shaped such that emitted electrons 62 are generallyemitted in a singular direction to assist in focusing of the electronbeam 64. In operation, the cathode emitter 50 of the beam injector 44may produce a focused and stable electron beam 64 that strikes thetarget 52 to produce radiation 40. As should be appreciated, the target52 may be of any suitable material, for example titanium or tungsten, toproduce the desired form of radiation in response to the incomingelectron beam 64. Although discussed herein as pertaining to electrons62 having a negative charge and forming an electron beam 64, it shouldbe appreciated that the emitted charged particle beam may be of anydesired charged particle, and, consequently, the relative potentials(e.g., voltages) discussed herein may also be reversed, for example, ifthe desired charged particle included a positive charge.

In some embodiments, the cathode emitter 50 may be biased with arelatively negative potential (e.g., voltage). In contrast, the target52 may have a positive potential relative to the cathode emitter 50. Assuch, the potentials of the cathode emitter 50 and/or the target 52 mayform an electric field in which electrons 62 may accelerate toward thetarget 52. Additionally or alternatively, the electrodes 58 of theparticle accelerator 46 may generate electric fields in which theelectrons 62 of the electron beam 64 may accelerate toward the target52. As such, the electron beam 64 may accelerate from the low and/ornegative voltage potential of the cathode emitter 50 toward the higherand/or positive voltage potential of the target 52. The acceleratedelectrons 62 of the electron beam 64 may then impact the target 52, andcause the target 52 to give off radiation 40. As should be appreciated,as used herein, electric fields may also generally encompass magneticand/or electromagnetic fields depending on reference frame.

In some embodiments, the beam injector 44 may also include a focusingchamber 56. The electrodes 58 within the focusing chamber 56 may assistin improving beam optics by generating electric fields to focus theelectron beam 64 like an optical lens. As should be appreciated, thefocusing chamber 56 and the acceleration chamber 54 may or may not havea discrete separation. Furthermore, the electrodes 58 of theacceleration chamber 54 and the focusing chamber 56 may be interlacedand/or serve both purposes.

The beam injector 44 may also include a Wehnelt electrode 66 maintainedat a relatively negative potential relative to the cathode emitter 50.While the potentials of the target 52, cathode emitter 50, and/orparticle accelerator 46 may motivate the electrons 62 to depart thecathode emitter 50 and accelerate towards the target 52, the Wehneltelectrode 66 may bias the electrons 62 to remain on the cathode emitter50 and/or assist in focusing of the electron beam 64 by forcing theemitted electrons 62 towards the center of the beam injector 44. Thenegative bias of the Wehnelt electrode 66 may suppress the emission ofelectrons 62 such that the majority of electron emissions are at thecenter of the cathode emitter 50 relative to the Wehnelt electrode 66,thus, improving focus of the electron beam 64. In one embodiment, theWehnelt electrode 66 may have a self-regulated potential based, at leastin part, on the beam current of the electron beam 64. For example, asthe beam current is increased, the negative potential of the Wehneltelectrode 66 may become more negatively biased, thus, confining and/orstabilizing the electron beam 64 and improving beam optics.

To help illustrate, FIG. 4 is a schematic diagram of three operationalregimes of the beam injector 44 with associated potential lines 68 aswell as a cathode heater current 70, beam focus 72, and beam current 74at each of the operational regimes. The potential lines 68 may be, ingeneral, indicative of the summed electric fields as influenced by, forexample, the potential of the cathode emitter 50, the potential of thetarget 52, the potential of the Wehnelt electrode 66, and/or thepotentials of the electrodes 58 within the focusing chamber 56 and/orthe acceleration chamber. Additionally, the “net zero” potential line 76of the potential lines 68 is graphically illustrated for each of thethree operational regimes to show the area of the surface 78 of cathodeemitter 50 that is in an emissive state (e.g., likely to emit electrons62), based on the surrounding electric fields.

For example, in the first operational regime 80, the magnitude of thenegative potential on the Wehnelt electrode 66 is relatively low, andthe potential lines 68 extend beyond the surface 78 of the cathodeemitter 50, such that a wide area of the surface 78 is in the emissivestate and likely to emit electrons 62. In other words, the “net zero”potential produced by the potential of the Wehnelt electrode 66 isbehind the surface 78 of the cathode emitter 50. As such, electrons 62on the surface 78 of the cathode emitter 50 with sufficient energylevels (e.g., relative to the work function of the cathode emitter 50)may be emitted. Since a wide area of the surface 78 is located in apositive electric field (e.g., in front of the net zero potential line76) electrons 62 may be emitted from the wide area of the surface 78,which may lead to a wide electron beam 64 having relatively poor beamfocus 72.

As the cathode heater current 70 is increased, the number of electrons62 with enough thermal energy to overcome the work function of thecathode emitter 50 may also increase. As such, more electrons 62 may beemitted, thus, increasing the beam current 74. In one embodiment, thenegative potential of the Wehnelt electrode 66 may be directly orindirectly related to (e.g., proportional to) the beam current 74. Assuch, as the cathode heater current 70 is increased, the magnitude ofthe negative potential of the Wehnelt electrode 66 (e.g., the Wehneltpotential) may also increase due to the increased beam current 74.Further, the increase in the magnitude of the Wehnelt potential mayshift the net zero potential line 76 towards the surface 78 of thecathode emitter 50 and decrease the area of the surface 78 in theemissive state, as in the second operational regime 82. By moving thenet zero potential line 76, such that a smaller area of the surface 78is in the emissive state, the beam focus 72 may be improved. As shouldbe appreciated, if the net zero potential line 76 were to continuemoving off of the surface 78 of the cathode emitter 50 the Wehneltpotential may “pinch” off the electron beam 64, and the beam current 74may be effectively zero.

In one embodiment, the Wehnelt electrode 66 may self-regulate theWehnelt potential, based on the beam current 74, to obtain and maintaina saturated beam current 74 with respect to the cathode heater current70, as in the third operational regime 84. The third operational regime84 may occur when the relation between beam current 74 and the Wehneltpotential on the Wehnelt electrode 66 reaches saturation such that afurther increase in the cathode heater current 70 may no longer affectan increase in beam current 74. For example, due to the self-regulationof the Wehnelt potential, a further increase in beam current 74 mayresult in an increased Wehnelt potential, which, in turn, would furthermove the net zero potential line 76 away from the surface 78 of thecathode emitter 50 and begin to pinch the electron beam 64, thus,decreasing the beam current 74. As such, the third operational regime 84may define an equilibrium state for a given state of the cathode emitterpotential, the Wehnelt potential (e.g., as driven by the emittedcurrent), target potential, and potentials of the electrodes 58 withinthe focusing chamber 56 and/or the acceleration chamber 54.

FIG. 5 is a schematic circuit diagram 86 of one embodiment of the beaminjector 44 that self-regulates the Wehnelt potential, U_(Wehnelt), onthe Wehnelt electrode 66. In one embodiment, a Wehnelt resistor 88 maybe implemented between the cathode emitter 50 and the Wehnelt electrode66. As such, the magnitude of the Wehnelt potential, relative to thecathode emitter potential, may be given by the total current, I_(Total),through the Wehnelt resistor 88 multiplied by the resistance of theWehnelt resistor 88, R_(Wehnelt), as shown in EQ. 1, which is indicativeof Ohm's Law.

U _(Wehnelt) =I _(Total) *R _(Wehnelt)  EQ. 1

In general, the electrodes 58 of the focusing chamber 56 and/or theacceleration chamber 54 may be separated by one or more resistors inseries or parallel to maintain the desired potentials of each electrode58. As such, the portion of the circuit diagram 86 through the focusingchamber 56 and/or the acceleration chamber 54 may be generalized by afocusing resistor 90 and an acceleration resistor 92. Further, the totalcurrent, I_(Total), may be a summation of the current through thefocusing resistor 90 and/or the acceleration resistor, I_(Bleed), aswell as the beam current 74, I_(Beam). As such, the Wehnelt potentialmay be given by, at least in a first order approximation,

U _(Wehnelt)=(I _(Bleed) +I _(Beam))*R _(Wehnelt).  EQ. 2

Accordingly, the Wehnelt potential, U_(Wehnelt), may be self-regulatedbased, at least in part, on the beam current 74, I_(Beam). As should beappreciated, the circuit diagram 86 is a simplified illustration, andfurther electrical components such as electrodes, capacitors, inductors,diodes, or resistors may also be included depending on implementation.

Additionally or alternatively, in some embodiments, the negativepotential of the Wehnelt electrode 66 may be regulated by a variablepower supply and/or Zener diodes. However, the use of a variable powersupply to directly control the Wehnelt potential may entail activemonitoring/adjustment, for example, by an additional power supply whichmay take up valuable real-estate or be impractical within the downholetool 12 depending on implementation. Furthermore, the use of a Zenerdiode may result in a fixed maximum potential of the Wehnelt electrode66 and/or limit the operational range of the beam current 74 whilemaintaining a focused electron beam 64 or limit the beam focus 72 atincreased beam currents 74. The use of the Wehnelt resistor 88 betweenthe Wehnelt electrode 66 and the cathode emitter 50 may allow for aself-regulated Wehnelt potential within the beam injector 44 that alsomaintains a desired amount of beam focus 72 throughout a range of beamcurrents 74.

In further illustration, FIG. 6 is a graph 94 of the beam current 74 andbeam focus 72 in relation to the cathode heater current 70 and theoperating potential 96. As stated above, as the cathode heater current70 increases, the beam current 74 may also increase causing the Wehneltpotential to also increase, thus, improving the beam focus 72. Aftersaturation 98, although the cathode heater current 70 may be increased,the beam current 74 and beam focus 72 may remain approximately constant.Additionally, in some embodiments, the operating potential 96 (e.g., thepotential of the cathode emitter 50, the potential of the target 52,and/or potentials within the particle accelerator 46) may be increasedto alter the potential lines 68 and motivate the net zero potential line76 into the cathode emitter 50 to increase the beam current 74.Accordingly, the Wehnelt potential of the Wehnelt electrode 66 may beautomatically regulated to maintain beam focus 72. As such, theself-regulated beam injector 44 may maintain beam focus 72 at variousbeam currents 74, depending, for example, on the value of the Wehneltresistor (R Wehnelt). Additionally, spikes and/or surges in beam current74 may be minimized due to the immediate change in Wehnelt potential aswell as the beam current's negligible response to additional cathodeheater current 70 after saturation 98.

The desired value for the Wehnelt resistor 88 of the beam injector 44may be determined based on the desired beam focus 72 and desired beamcurrent 74 at a desired range of operating potential 96. For example, ata particular operating potential 96, a smaller Wehnelt resistor 88 valuemay correspond to a wider electron beam 64 and/or a higher beam current74. Likewise, at the same operating potential 96, a larger Wehneltresistor 88 value may correspond to a narrower electron beam 64 and/or asmaller beam current 74. Additionally, in some embodiments, the Wehneltresistor 88 may allow for increased efficiency (e.g., decreasedcomplexity and time consumption) during calibration of the beam injector44 and/or the radiation apparatus 38 by reducing the calibration to theadjustment of the Wehnelt resistor 88.

FIG. 7 is a flowchart 100 of an example process for calibrating andoperating the beam injector 44. The beam injector 44 may be operatedwith an initial estimated Wehnelt resistor 88 value corresponding to thedesired operating potential 96, beam focus 72, and/or beam current 74(process block 102). The cathode heater current 70 may then be increaseduntil saturation 98 is achieved (process block 104). The beam current 74may be analyzed to determine if the desired beam current 74 is achievedat the desired operating potential 96 (decision block 106). If thedesired beam current 74 is achieved, the beam injector 44 may beoperated at the desired operating potential 96 (process block 108). Ifthe desired beam current 74 is not achieved, the Wehnelt resistor 88value may be adjusted (process block 110). For example, if the beamcurrent 74 is determined to be less than desired, the Wehnelt resistor88 value may be reduced to reduce the magnitude of the Wehneltpotential. Moreover, if the beam current 74 is determined to be greaterthan desired, the Wehnelt resistor 88 value may be increased. Afteradjustment the cathode heater current 70 may be increased untilsaturation 98 (process block 104) and the beam current 74 may bedetermined again (process block 106). As should be appreciated, althoughthe above referenced flowchart 98 is shown in a given order, in certainembodiments, the depicted decision and process blocks may be reordered,altered, deleted, and/or occur simultaneously. Additionally, thereferenced flowchart 100 is given as an illustrative tool, and furtherdecision and/or process blocks may be added depending on implementation.

As discussed above, in some embodiments, the beam injector 44 mayinclude a cathode emitter 50, which may be heated to emit electrons 62or other ions. Heating of the cathode emitter 50 may be accomplished byapplying a voltage to the heating element 60. In some embodiments, theheating element 60 may be powered via a cathode driver 112, and thehigh-voltage applied to the cathode emitter 50 may be supplied via ahigh-voltage driver 114 augmented by a voltage multiplier 116, forexample as depicted in FIG. 8. The voltage multiplier 116 may includeone or more ladder sections 118 and a boosting coil 119. The boostingcoil 119 may cause resonance within the ladder sections 118 to increasethe voltage level output and efficiency of the voltage multiplier 116.Additionally, the cathode driver 112 may utilize a cathode isolationtransformer 120 utilizing a set of primary coils 122 and secondary coils124 around a magnetic core 126. The cathode isolation transformer 120may facilitate power to the heating element 60 without routing thecathode power lines 128 in close proximity to the voltage multiplier116, which may produce strong electric fields that could lead toelectrical events such as arcing, tracking, field emission, and/orcorona effects.

As should be appreciated, the high-voltage driver 114, cathode driver112, voltage multiplier 116, and/or isolation transformer 120 may bedisposed within an enclosure 130 of the downhole tool 12, along with oneor more insulators 132 and/or the radiation apparatus 38. In an effortto decrease the size of the enclosure 130, in some embodiments, theisolation transformer 120 may be replaced by a step down transformer 134at the high-voltage end 136 of the voltage multiplier 116, for exampleas depicted in FIG. 9. As such, the high-voltage driver 114 may providethe power to the heating element 60 instead of a dedicated cathodedriver 112, may increase electrical efficiency as well as spatialefficiency.

Additionally, in some embodiments, the boost coil 119 may be utilized asboth a boost coil 119 and a step down coil. For example, the boost coil119 may be wrapped around a magnetic core 126 and one or more additionalstep down coils 138 may step the voltage level down such that thevoltage differential at the heating element 60 is within the operatingrange of the heating element 60. In some embodiments, the step downtransformer 134 may reduce the voltage of the heating element 60 towithin the operating range relative to a ground reference, relative tothe high-voltage output of the voltage multiplier, or relative to avoltage level in between.

FIG. 10 is a flowchart 140 of an example process for powering aradiation apparatus 38. The voltage multiplier 116 may receive an inputpower from the high-voltage driver 114 (process block 142). The voltagemultiplier 116 may then increase the voltage of the input power (processblock 144) and apply a high voltage to the cathode emitter 50 and a stepdown transformer 134 (process block 146). For example, in someembodiments, a boosting coil 119 and the frequency of the input powermay be tuned to resonate to generate a large high voltage (e.g., greaterthan 50 kV, greater than 100 kV, or greater than 400 kV) with a highefficiency (e.g., greater than 70 percent efficient, greater than 80percent efficient, or greater than 90 percent efficient). One or morestep down coils 138 may reduce (e.g., step down) the high voltage(process block 148), and the stepped down voltage may be applied to theheating element 60 (process block 150). Additionally, in someembodiments, the beam current may be regulated (process block 152), forexample by the beam injector 44.

As stated above, the step down transformer 134 may eliminate theisolation transformer 120 and the dedicated cathode driver 112, whichmay assist in reducing the size of the enclosure 130 and/or increasingthe available space for insulation 132, which may facilitate increasedoperating voltages and thus increased radiation output. Additionally, insome embodiments, the step down transformer 134 may have a higherefficiency than the isolation transformer 120 leading to reduced powerconsumption.

In one embodiment, the isolation transformer 120 and the dedicatedcathode driver 112 may also be removed with the use of a cold cathode(e.g., without the use of a heating element 60). In some scenarios, coldcathodes may be difficult to operate with consistent radiation output.For example, a ruggedized, field emission-based cathode may havevariations in output due to fluctuations in current from the wearingdown of the field emissive layers. However, the self-regulation of thebeam injector 44 may provide consistent operation of the cold cathode,and, therefore, facilitate the reduction in size of the enclosure 130 byremoving the isolation transformer 120 and the dedicated cathode driver112. Indeed, in some embodiments, the radiation apparatus housing 48and/or the voltage multiplier may also be reduced in size to furtherreduce the size of the downhole tool 12.

In some embodiments, the enclosure 130 may be reduced to less than 5inches, less than 3 inches, or less than 2 inches in diameter. Forexample, the housing 48 of the radiation apparatus 38 (e.g., theelectron accelerator 46) may be less than 1.5 inches, less than 1.0inches, or less than 0.8 inches in diameter. Additionally, in someembodiments, voltage multiplier 116 may be reduced to less than 1.5inches, less than 1.0 inches, or less than 0.8 inches in diameter. Forexample, the voltage multiplier 116 may include a single layer ofcapacitors to reduce the diameter.

Additionally, in some embodiments, the insulation 132 may include aninsulating gas (e.g., air, sulfur hexafluoride (SF6), etc.), a highdielectric insulator (e.g., perfluoroalkoxy (PFA), fluorinated ethylenepropylene (FEP), and/or plastic, Kapton, or Teflon materials), shieldingrings (e.g., corona rings), and/or potting material. Shielding rings maybe implemented in a co-axial arrangement around the voltage multiplier116 and/or the radiation apparatus 38 to reduce the electric fieldstresses proximate the electrical components (e.g., capacitors, diodes,etc.) of the downhole tool 12. In one embodiment, the shielding ringsmay be generally conductive and made of any suitable metallic materialor other conductor. Further, in one embodiment, the shielding rings maybe made of a semiconductor plastic. In some embodiments, the multiplierstages of the voltage multiplier 116 may be electrically connected toindividual shielding rings spaced axially apart and radially around theelectrical components. By maintaining the shielding rings atapproximately the same potential as the electrical components within thecircumference of the shielding rings, the electric fields andcorresponding electric field stresses and, therefore, electrical eventswithin the shielding rings may be reduced. Furthermore, the pottingmaterial may have a conductivity greater than 10⁻¹⁶ S/m and/or aconductivity less than 10⁻⁴ S/m, less than 10⁻⁸ S/m, or less than 10⁻¹³S/m such as boron nitride with a silicon elastomer (e.g., Sylgard). Insome embodiments, the potting material may be more conductive than thedielectric insulator and/or the shielding rings. The potting materialmay form a cylindrical tube around the electrical components or othersuitable shape conforming to the shape of the housing 48 and/orenclosure 130.

Although the present disclosure has generally discussed the beaminjector 44 and step down transformer as utilized with the radiationapparatus 38 of the downhole tool 12, the systems and methods of thisdisclosure may be applied to any charged particle beam-formingelectronic device where the size of the enclosure 130 and/or stabilityof beam optics and/or beam current is of concern.

The specific embodiments described above have been shown by way ofexample, and it should be understood that these embodiments may besusceptible to various modifications and alternative forms. It should befurther understood that the claims are not intended to be limited to theparticular forms disclosed, but rather to cover modifications,equivalents, and alternatives falling within the spirit and scope ofthis disclosure.

1. An apparatus comprising: a power supply configured to receive a firstvoltage potential and output a second voltage potential, wherein thesecond voltage potential is greater than the first voltage potential; acathode emitter configured to: receive the second voltage potential; andin response to application of the second voltage potential, emit ions; astep down transformer configured to receive the second voltage potentialand output a third voltage potential, wherein the third voltagepotential is less than the second voltage potential; and a heatingelement configured to: receive the third voltage potential; and inresponse to application of the third voltage potential, heat the cathodeemitter to lower a work function of the cathode emitter.
 2. Theapparatus of claim 1, wherein the power supply comprises a voltagemultiplier.
 3. The apparatus of claim 2, wherein the power supplycomprises a boosting coil configured to resonate with the voltagemultiplier.
 4. The apparatus of claim 3, wherein the step downtransformer comprises at least two coils, wherein a first coil of the atleast two coils comprises the boosting coil.
 5. The apparatus of claim1, wherein the step down transformer comprises a magnetic core and aplurality of conductive coils.
 6. The apparatus of claim 5, wherein atleast one coil of the plurality of coils is shared with the powersupply.
 7. The apparatus of claim 1, wherein the second voltagepotential is greater than 50 kilovolts (kV) relative to a groundreference.
 8. The apparatus of claim 1, comprising regulator circuitryconfigured to regulate an ion beam current.
 9. The apparatus of claim 8,wherein the regulator circuitry comprises: an electrode configured tobias at least a portion of the ions to remain on the cathode emitter;and a resistor coupled between the cathode emitter and the electrode andconfigured to allow self-regulation of a fourth voltage potential on theelectrode based at least in part on the ion beam current.
 10. Theapparatus of claim 9, wherein the electrode is configured to focus theemitted ions into an ion beam.
 11. The apparatus of claim 1, wherein theemitted ions are aimed at a target, wherein the target is configured toemit radiation in response to the ions hitting the target.
 12. Theapparatus of claim 11, wherein the radiation comprises x-ray radiation.13. The apparatus of claim 1, wherein the heating element is configuredto receive the second voltage potential such that the heating element ispowered via a voltage difference between the second voltage potentialand the third voltage potential.
 14. A method comprising: receiving apower input at a first voltage potential; increasing, via a voltagemultiplier, the first voltage potential to a second voltage potential;decreasing, via a transformer, the second voltage potential to a thirdvoltage potential; providing the second voltage potential to a cathodeemitter configured to emit ions; and providing the third voltagepotential to a heating element of the cathode emitter.
 15. The method ofclaim 14, wherein the transformer comprises a plurality of step downcoils disposed around a magnetic core.
 16. The method of claim 15,wherein a coil of the plurality of step down coils is configured toresonate with the voltage multiplier to increase the second voltagepotential relative to the first voltage potential.
 17. The method ofclaim 14, comprising regulating, via regulator circuitry, an ion beamcurrent of the cathode emitter, wherein the regulator circuitrycomprises an electrode configured to bias at least a portion of the ionsto remain on the cathode emitter.
 18. A downhole tool comprising: aradiation apparatus comprising: a cathode emitter configured to emitelectrons; an electrode configured to bias at least a portion of theelectrons to remain on the cathode emitter and focus the emittedelectrons into an electron beam; and a resistor coupled between thecathode emitter and the electrode and configured to allowself-regulation of an electrode potential on the electrode based atleast in part on a current of the electron beam; and a high-voltagepower supply comprising a voltage multiplier and configured to supplypower to the cathode emitter at a voltage potential.
 19. The downholetool of claim 18, comprising: a heating element configured to heat thecathode emitter; and a step down transformer configured to step down thevoltage potential of the power to a second voltage potential to besupplied to the heating element.
 20. The downhole tool of claim 18,wherein the cathode emitter comprises a field emission-based cathode.